Destroying and recovering spiral vortex beams due to figured perturbations

Abstract

Using asymptotic approaches and an experiment supported by computer simulation, we examined transforming spiral vortex (SV) beams caused by affecting figured hard-edged apertures. By the example of a tetragonal beam, we considered three perturbation scenarios: (1) asymmetric perturbation, when an opaque screen covers the caustic only on one side of the tetragon, (2) symmetric perturbation, when the figured aperture covers the entire beam except for a narrow caustic region, and (3) symmetric perturbation when the figured aperture screens only the caustic region without affecting the rest of the beam. At the same time, we carried out asymptotic calculations for all types of polygonal beams. It was found that the beam can partially restore its original state if the aperture does not touch the caustic region. Otherwise, the former SV beam structure is destroyed, but a new stable state appears in a far diffraction zone.